1. Field of the Invention
The present invention relates to a magnetron sputtering cathode, a magnetron sputtering apparatus, and a method of manufacturing a magnetic device.
2. Description of the Related Art
Sputtering processes using ferromagnetic materials are routinely utilized for manufacturing magnetic heads, such as GMR and TMR heads, MRAM devices, and inductors.
In a manufacturing process in a vacuum, such as a sputtering process, it has conventionally been regarded as important to improve the operating rate and to reduce the manufacturing cost by reducing the maintenance time required for the exchange of targets as much as possible. Because of this reason, a method has been searched for, which lengthens the target lifetime by increasing the thickness of the sputtering target itself and increases the operating rate.
In magnetron sputtering, a cathode magnet is provided behind a sputtering target so that a closed circuit magnetic field “tunnel” is formed on the discharge surface of the sputtering target.
In the above-mentioned sputtering process, in particular, in the process for manufacturing a magnetic head, a sputtering target made of a ferromagnetic material, such as an alloy of iron and cobalt and an alloy of nickel and iron, is used. Since these ferromagnetic targets have very high magnetic permeability and saturation magnetic flux density, even if a cathode magnet is installed behind a sputtering target made of a ferromagnetic material, almost all of the magnetic lines of force pass through the inside of the ferromagnetic target, and therefore, no magnetic tunnel is formed on the target discharge surface and a sufficient magnetic field strength cannot be obtained.
In order to solve the above-mentioned problem, a conventional sputtering cathode has employed a method of optimizing the shape of a target so that magnetic lines of force can be generated efficiently from a cathode magnet placed behind the target to the front of the target.
Japanese Publication of Patent Application No. 2005-509091 has proposed a method of confining a magnetic field between auxiliary targets by dividing a target into a plurality of regions of the auxiliary targets and a main target and making the height of the auxiliary target greater than that of the main target.
However, as a result of a simulation conducted to evaluate the magnetic field on a target surface by applying the method according to Japanese Publication of Patent Application No. 2005-509091 to a target of a material having high saturation magnetic flux density, for example, an iron-cobalt alloy (saturation magnetic flux density is 2.4 Tesla), almost all the magnetic lines of force pass through inside of the main target and the magnetic field component parallel to the surface of the main target became very small.
Conventionally, it has been required to increase the thickness of a target in order to improve the tool utilization (operating rate) by lengthening the target lifetime, however, as described above, the magnetic field on the target discharge surface (sputtering surface) becomes smaller with increasing thickness of the target, and the leakage magnetic field will disappear soon. That is, if the thickness of a target is increased, the target lifetime is lengthened, and therefore, the exchange span of the target is also lengthened and the operating rate is improved as a result, however, if the thickness of a target is increased, the magnetic field that leaks out from the target will decrease or disappear. Because of this, there has conventionally been a limit to achieving both the formation of a sufficient magnetic field on the target discharge surface and the lengthening of the target lifetime.
Further, conventionally, it has been difficult to cause a sufficient magnetic field to leak out to the target discharge surface even by using the method described in Japanese Publication of Patent Application No. 2005-509091 when a ferromagnetic body having high magnetic permeability and saturation magnetic flux density is used as a target.